Cylinder blocks for internal combustion engines are typically formed with numerous internal cavities and passages which serve a variety of purposes. Included among these are push rod passages extending between an upper valley of the cylinder block and an internal camshaft gallery for accommodating the engines push rods and tappets. To lubricate these passages, an engine is typically provided with a pair of long and narrow oil galleries which communicate with each of these passages. Such passages are typically machined into the block following casting. When forming the oil gallery in this manner, it is usual practice to drill the gallery from opposite ends of the block so as to form a through passage completely through the block. One end of the passage is left open for admitting lubricating oil into the oil gallery while the other end must be plugged. Experience has shown that such plugs tend to loosen over time and leak. Once the engine is installed in an automobile, these plugs are usually difficult to access and repair.
Various casting cores have been proposed for forming long and narrow fluid passages in cylinder blocks. Examples of such cores include those disclosed in U.S. Pat. Nos. 2,991,520 to Dalton, granted Jul.11, 1961; 3,945,429 to Wahlqvist, granted Mar. 23, 1976; and 4,829,642 to Thomas et al, granted May 16, 1989.
The Thomas patent teaches casting a stainless steel tube within a cylinder block. Such tubes, however, are expensive to manufacture and add to the cost and complexity of manufacturing a cylinder block. It is necessary to inspect the surfaces of the tubes to assure that it is clean and free from any foreign materials which would form porosity or inclusions in the casting or prevent the casting metal from completely surrounding the tube.
The Dalton and Wahlqvist patents disclose forming a casting core with a central metal support element surrounded by a sheath of refractory material, such as fiberglass sleeving or bonded foundry sand. These cores, however, form a fluid passage that extends completely through opposite ends of the article and at such would suffer from the same detriments such as alluded to above for drilled-in oil galleries.